Measurement of the concentration of various substances in a blood sample is important for diagnosis of various diseases or judgment of the treatment process. For example, measurement of substances such as cholesterol, uric acid, glucose, triglyceride, phospholipid, choline, creatine, creatinine, free cholesterol, and cholesterol ester in the blood is important. As a method for measuring them, widely used is a method (enzymatic method using an oxidizable color reagent) in which an oxidase is applied to these components or a derivative of these components, and hydrogen peroxide generated directly or indirectly from the enzymatic reaction is applied to an oxidizable color reagent, which is a coloring reagent of the hydrogen peroxide, and then the generated color is quantified.
However, reducing substances such as bilirubin, hemoglobin, and ascorbic acid exist in a blood sample, and existence of these substance greatly affect measurement values of the substances in the blood sample, which may cause errors in the measurement values. In addition, it is known that, for example, bilirubin or hemoglobin which also acts as a coloring matter causes errors depending on a measurement wavelength, and absorption of these coloring matters themselves temporally changes during the measurement because of the existence of, for example, light and components in the measurement reagent, and affects the measurement results.
As a method for avoiding the influences of bilirubin, among the above components, known is a method in which an amphoteric surfactant is added to a measurement reagent. For example, Patent Literature 1 describes that an amphoteric surfactant is added to a first reagent for the purpose of avoiding the influences of bilirubin. Patent Literature 2 describes a method for measuring a bio-component by detection of hydrogen peroxide produced from the enzymatic reaction with peroxidase and an oxidizable coloring agent in which an amphoteric surfactant and a ferrocyanide compound are allowed to exist together with a first reagent or both of the first reagent and a second reagent.
Further, Patent Literature 3 describes a method for measuring a substrate or an enzyme activity in the body fluid, in which an amphoteric surfactant (only alkyl betaine oxide (product name: AMPHITOL 20N) as used in Examples) is allowed to co-exist with a first reagent or a second reagent in a measurement system for the purpose of avoiding the influences of hemoglobin or/and bilirubin existing in the body fluid. However, in Patent Literature 3, there is no Example investigating the influences of both of total hemoglobin and bilirubin in the reagent at the same time under existence of the amphoteric surfactant. In addition, Patent Literature 4 describes a method using a peroxide and a non-ionic surfactant or/and an amphoteric ion surfactant as a method for avoiding the influences of both of hemoglobin and bilirubin. However, in Patent Literature 4, adjustment of the reagent is complicated such that the surfactant needs to be treated with, for example, light irradiation, and the peroxide concentration needs to be adjusted to a certain quantity.